1. Field of Invention
This invention relates generally to the treatment of tinnitus disorders, and in particular to an electronic stimulation system in which a complex signal in the sonic range is applied to an electrodynamically-actuated diaphragm and probe assembly, acting as an applicator, to cause the probe to vibrate in accordance with the signal and to cause the diaphragm to audibly reproduce the signal. The vibrations of the probe are transmitted to the cochlea of the inner ear of the patient to mask internal tinnitus sounds heard by the patient.
2. Status of Prior Art
The human ear functions as an auditory system for converting incoming sound vibrations into electrical energy which triggers nerve impulses in the auditory nerve connected to the brain. In this auditory system, sounds picked up by the outer ear (auriole) are conducted through an auditory canal to a tympanic membrane or eardrum. The middle ear which is separated from the outer ear by the eardrum, contains three small bones which as sounds strike the eardrum are then caused to vibrate. These bone vibrations set up corresponding vibrations in an oval window from which the vibrations are conveyed to the three fluid-filled canals contained in the cochlea of the inner ear.
At the base of the central canal of the cochlea is a basilar membrane, and supported on this membrane is the organ of Corti and its hair cells. These cells are the true receptors of hearing, for proliferations from the fibers of the auditory nerve extend up the center of the cochlea and connect with these hair cells.
Auditory sounds vary in frequency throughout the audio spectrum. The ability to hear many different frequencies as distinct pitches is related to the ability of the cochlea to resolve these frequencies. In the range of about 200 to 2000 Hz this resolution is effected by differential response of the basilar membrane. The cochlea has different resonance values at different points along its length. Hence high tones cause the fluid of the cochlea and the membrane to vibrate near the base, while low tones cause these to vibrate near the apex.
The concern of the present invention is with the treatment of tinnitus disorders. Tinnitus aureum, in Latin, literally means "ringing of the ears" and is a common symptom in adults. Though the term refers to sounds originating in the ear, they may not be ringing in nature, for buzzing, humming, whistling and roaring sounds are also indicative of a tinnitus disorder.
A more precise definition of tinnitus is any sound sensation for which there is no source outside of the individual. According to the text Principles of Neurology by Adams & Victor-McGraw Hill (Third Edition). "For most forms of tinnitus, there is little effective treatment." Yet despite this negative approach to tinnitus, the prior art discloses various attempts to overcome this condition.
Thus the Westerman U.S. Pat. No. 5,325,872 (1994) discloses an electronic system for treating tinnitus in which the outputs of two voltage-controlled oscillators operating in the sonic range are combined and amplified. The resultant signal is applied to an ear piece placed on the outer ear of the patient. Hence what the patient hears is a therapeutic tone whose frequency repeatedly and slowly scans throughout a frequency range which contains the tinnitus ringing tone. According to Westerman, because the therapeutic tone with each scan repeats the ringing frequency, this acts to mask or suppress the ringing frequency.
A similar approach is taken by Gooch in U.S. Pat. No. 5,403,262 (1996) in which applied to the ear of a patient suffering from a tinnitus ringing sound is a tone of a frequency which masks the tinnitus ringing sound and overrules this sound.
The effectiveness of these prior approaches is believed to be of limited value in the treatment of tinnitus in that the therapeutic tones are applied to the outer ear of the nerve cells responsible for the tinnitus condition.
In the nerve center associated with the brain which is responsible for processing sounds, each individual nerve cell located in the uppermost level of the eight cranial nerve is stimulated only by a sound having a specific frequency. It is therefore the task of the multitude of nerve cells in the uppermost level of the eigth nerve to inform the brain that specific sounds or tones are being heard, or that a complex tone or a mixture of sounds are being heard. Hence each nerve cell in the nerve center has an assigned task.
The reason therefore a patient suffering from tinnitus has the sensation of hearing a ringing tone made up of specific frequencies is that the nerve cells that normally hear and transmit to the brain a really audible tone composed of these frequencies are being artificially stimulated, and may remain in this condition for a prolonged period. The cause of this faulty stimulation is not known. But what is known is that a substantial percentage of adults throughout the world suffer from tinnitus.
Inasmuch as the nerve center associated with the brain is the source of tinnitus disorders, and in the human auditory system, it is the cochlea that conducts impulses to this nerve center, in a system in accordance with the invention to treat tinnitus, it is the cochlea that is stimulated.
Our prior Di Mino patent 5,788,656 discloses an electronic stimulation system for treating a patient suffering from a tinnitus disorder; the system acting to transmit vibrations in the sonic range to the cochlea of the inner ear. The system includes an electromagnetically-actuated probe to which is applied a complex signal in the auditory range to cause the probe to vibrate in accordance with the signal, the probe being placed at a position on the patient in proximity to the cochlea of the inner ear whereby the probe vibrations are transmitted to the cochlea.
The mechanical vibrations conveyed by the probe in accordance with the complex signal in the sonic range actuating the probe must be properly related to the internal tinnitus sounds being heard by the patient being treated. It is only when this proper relationship exists, that the tones produced externally by the complex signal acts to mask and in time suppress the internal tinnitus sounds.
In the system disclosed in the prior Di Mino patent, the complex signal actuating the probe is generated by two audio-frequency oscillators, one operating in a low-frequency range whose upper limit is 400 Hz, the other in a higher frequency range whose upper limit is 1000 Hz. The resultant complex signal therefore includes the negative and positive beats of the two oscillator frequencies.
It is only the patient being treated who hears the internally-generated tinnitus sounds. In order therefore to produce a complex signal which is appropriate to an existing tinnitus condition and functions to mask the tinnitus sounds, it is the patient hearing the tinnitus sounds who must determine which complex signal is effective in treating his condition.
In order therefore for a system of the type disclosed in our prior Di Mino patent to be effective, it is essential that the two oscillators which together generate the complex signal be adjusted so that the resultant vibrations of the probe applied to the cochlea of the patient's ear then act to mask the internally-generated tinnitus sounds heard by the patient being treated.
But for the patient to be able to properly adjust the two oscillators, the complex signal must be reproduced so that it can be clearly heard by the patient. Then as the patient adjusts the oscillators, he can hear the resultant complex signal and determine which form of complex signal acts to effectively mask the internally-generated tinnitus sounds.
The practical drawback of the system disclosed in the Di Mino patent is that it does not adequately audibly reproduce the complex signal, and the patient therefore may have difficulty in adjusting the oscillators to generate the particular complex signal which is most effective in masking the tinnitus sounds.